1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, a method for producing an electrophotographic photosensitive member, a process cartridge, and an electrophotographic apparatus.
2. Description of the Related Art
An electrophotographic photosensitive member repeatedly used in an electrophotographic apparatus desirably has high wear resistance. Japanese Patent Laid-Open No. 2000-066425 describes a technique of improving the wear resistance of an electrophotographic photosensitive member. According to this technique, a polymerized product obtained through polymerization of a charge transporting compound having a chain polymerizable functional group is added to a surface layer of the electrophotographic photosensitive member. Japanese Patent Laid-Open No. 2000-066425 teaches that an acryloyloxy group and a methacryloyloxy group are particularly favored as the chain polymerizable functional group.
As the wear resistance of the electrophotographic photosensitive member is improved, it becomes more difficult to refresh the surface of the electrophotographic photosensitive member. The material that has undergone chemical changes by repetitive use tends to remain on the surface of the electrophotographic photosensitive member. Discharge products generated through a charging process that involves discharging are thought to be the main cause of the chemical changes of the materials constituting the surface of the electrophotographic photosensitive member. In particular, when one of the materials constituting the surface of the electrophotographic photosensitive member is a charge transporting compound (also refers to a polymerized product of a charge transporting compound, the same applies hereinafter), the charge transporting compound serves as a donor and NOx, which is a type of discharge products, serves as an acceptor, thereby readily generating DA ion pairs. Since DA ion pairs absorb light in the visible light region, the presence of the DA ion pairs is identifiable by visual observation or through visible absorption spectrum measurement. The DA ion pairs eventually form covalent bonds and the charge transporting compound (charge transporting structure) is thereby modified into a NOx-modified compound (refer to D. S. Weiss, J. Imag. Sci., 34, 132 (1990)).
Once the charge transporting compound (charge transporting structure) becomes modified, various properties of the photosensitive member are induced. For example, the modified part of the charge transporting compound (charge transporting structure) acts as a charge trap and may result in an increase in residual potential.